As for FM Yamahas, we connected YM2203 to ZX Spectrum. I have such a thing actually.

2203 has full (almost full?) AY/YM implementation + FM. It has 3 channels too.
However the output/input data uses different ports. So it was reuired to make an additional small board/convertor. We take out AY/YM and instead put inside the board with 2203 installed.

As we use TurboSound (2xYM) for many years, this one - TurboSoundFM - has also 2 YM2203 which gives 6 channels.

It sounds more/less like this -
http://velesoft.speccy.cz/turbo_sound/nedopc/tsfm-space_standart%20(shiru).mp3
and also can do much more.

Still, there are some problems. It doesn't like to play digital music and sometimes it's required to start digital music twice, without reset (only on the second time it works OK) which is a pity because not all programs can restart music (and sadly after reset it will work badly again).

Schemes are here, if anybody's interested.
http://velesoft.speccy.cz/turbosound-cz.htm
We have also a cross-platform editor to make such music for Spectrum, it's called TurboSoundFM Tracker.